A loudspeaker is an important acoustical component in a portable electronic device, is used for transforming electric signal into acoustical signal, and is an energy converter. The loudspeaker typically comprises a vibration system and a magnetic circuit system, the vibration system comprises a diaphragm assembly and a voice coil which are joined together, wherein the diaphragm assembly is an important component of the loudspeaker, which plays a vital role in the sound emission performance of the loudspeaker, and determines the conversion quality of the loudspeaker from electrical energy to sound energy. The existing diaphragm assembly comprises a silica gel diaphragm, and a dome is required to be joined to the middle of the diaphragm in order to adjust acoustic performance. As the silica gel diaphragm is relatively softer, an annular support member is further required to be fixed to the edge portion of the diaphragm. The structure of the existing diaphragm assembly is shown in FIG. 1, the diaphragm 20a comprises an annular bending portion, and a diaphragm center portion and a diaphragm edge portion provided at the inner and outer sides of the bending portion, respectively; the upper surface of the support member 40 and the lower surface of the diaphragm edge portion are bonded and fixed to each other via glue, and the dome 30 and the diaphragm center portion are fixed to each other via glue as well. Under the influence of the material of the silica gel diaphragm, such a bonding mode has poor bonding firmness and its stability is not high, and the product has poor consistency. During the operation of the loudspeaker, the silica gel diaphragm is extremely easy to be disengaged from the support member or the dome, which greatly reduces the stability and reliability of the loudspeaker, and greatly shorten the life of the loudspeaker as well.